The invention relates to an apparatus for radiation treatment for personal care, comprising a housing in which a UV source is present and a wall made from a UV-transmitting material which covers the housing, said wall having a central area and side areas adjoining the central area.
Such an apparatus for radiation treatment for personal care is generally known. If the apparatus is used as a suntanning apparatus, a user is present in an irradiation plane of the UV source extending in a longitudinal direction so as to achieve a tanning of the skin. The UV source used for this produces a comparatively large quantity of effective radiation with a wavelength in the range  less than 320 nm (UVB), which radiation is mainly responsible for tanning of the skin, and a comparatively small quantity of effective radiation with a wavelength in the range from 320 to 400 nm (UVA). The UV-transmitting wall has for its object to filter out a large quantity of radiation with a wavelength  less than 320 nm, such that the value of the effective radiation energy thereof does not exceed the value of 0.14 W/m2 (European standard EN 60335-2-27) in the irradiation plane. The natural distribution of the resulting effective radiation energy over the longitudinal direction of the irradiation plane is such that a substantially higher effective radiation energy is present in the central area of the irradiation plane than in the side areas of the irradiation plane. The effective radiation energy in the side areas of the irradiation plane is approximately 50% of the effective radiation energy in the central area of the irradiation plane during operation of the known apparatus. To obtain an even tanning, however, a homogeneous distribution of the effective radiation energy of the UV source over the longitudinal direction of the irradiation plane is desirable. A disadvantage of the known apparatus, therefore, is that an optimum homogeneous suntanning cannot be achieved with the apparatus.
A homogeneous distribution of the effective radiation energy of the UV source over the longitudinal direction of the irradiation plane can be realized in principle by means of specific optical properties of a reflector system adjacent the UV source, but this brings with it the consequence that the total radiation energy in the irradiation plane is comparatively low. It is true that such a reflector system spreads the radiation such that an effective radiation energy evenly distributed over the irradiation plane is achieved. At the same time, however, a substantial portion of the effective radiation energy falls outside the irradiation plane in this manner, which implies a loss of effective radiation energy. This means that a comparatively long suntanning time is required for obtaining an even tanning, which is not desirable.
It is an object of the invention to provide an apparatus of the kind mentioned in the opening paragraph with which a tanning of the skin which is as even as possible can be realized in a time period which is as short as possible.
The above object is achieved with an apparatus according to the invention which is characterized in that the wall has a lower transmission to radiation with a wavelength  less than 320 nm adjacent the central area than adjacent the side areas. The comparatively large quantity of radiation having a wavelength  less than 320 nm radiated by the UV source is better transmitted by the wall adjacent the side areas of the wall than adjacent the central area of the wall in this manner during operation of the apparatus. The transmission is such here that the effective radiation energy of radiation having a wavelength  less than 320 nm and incident on the lateral portions of the irradiation plane approximates the value of 0.14 W/m2 (European standard EN 60335-2-27), while the effective radiation energy of radiation having a wavelength  less than 320 nm and incident on the central portion of the irradiation plane also approximates this value. This results in a distribution of effective radiation energy of radiation having a wavelength  less than 320 nm which is substantially homogeneous viewed over the entire irradiation plane. An even tanning of the skin of a user of the apparatus can thus be realized without a long treatment period of the user in the irradiation plane being necessary.
An embodiment of an apparatus according to the invention is characterized in that the wall has a greater thickness adjacent the central area than adjacent the side areas. Since the wall is thicker adjacent the central area than adjacent the side areas, the wall has a lower transmission to radiation with a wavelength  less than 320 nm adjacent the central area than adjacent the side areas. A substantially homogeneous distribution of effective radiation energy of radiation having a wavelength  less than 320 nm over the irradiation plane during use is thus realized in a manner which is constructionally comparatively simple.
It is favorable in this respect if the wall comprises a layer in the form of a coating which has a greater thickness adjacent the central area than adjacent the side areas. A coating can be provided on the wall with a variable thickness in a comparatively simple manner in mass manufacture.
A further embodiment of an apparatus according to the invention is characterized in that the wall is manufactured from a first material having a comparatively high transmissivity to radiation with a wavelength  less than 320 nm, and a second material is provided adjacent the central area, which second material has a comparatively low transmissivity to radiation with a wavelength  less than 320 nm. As a result, the wall transmits a greater proportion of radiation having a wavelength  less than 320 nm at the side areas, whereas in the central area, where the second material is present, less radiation having a wavelength  less than 320 nm is transmitted. The transmission is such in this manner that the effective radiation energy of radiation with a wavelength  less than 320 nm reaching the side portions of the irradiation plane approximates the value of 0.14 W/m2 (European standard EN 60335-2-27), while the effective radiation energy of radiation with a wavelength  less than 320 nm reaching the central portion of the irradiation plane also approximates this value. This results in a substantially homogeneous distribution of effective radiation energy of radiation with a wavelength  less than 320 nm over the irradiation plane, so that an even tanning of the skin of a user of the apparatus can be realized without a long treatment time of the user in the irradiation plane being necessary.
It is advantageous here if the second material has a comparatively high transmissivity to radiation with a wavelength in the range from 320 to 400 nm. The UV source produces a small quantity of radiation in this range, which quantity, if fully transmitted by the wall, poses no risk to the user. Since the second material has a comparatively high transmissivity to radiation with a wavelength in the range from 320 to 400 nm, this radiation is transmitted to the central portion of the irradiation plane to a substantial degree, which contributes to an optimum utilization of this radiation.
It is furthermore advantageous if the second material is provided in a predetermined pattern. In that case the material can be provided on the wall in a comparatively simple manner during manufacture.
A further embodiment of an apparatus according to the invention is characterized in that intermediate areas are present between the central area and the side areas, in which intermediate areas the wall has a transmission to radiation with a wavelength  less than 320 nm which lies between the transmission adjacent the central area and the transmission adjacent the side areas. The intermediate areas contribute further to the realization of a substantially homogeneous distribution of effective radiation energy of radiation with a wavelength  less than 320 nm over the irradiation plane.
A further embodiment of an apparatus according to the invention is characterized in that the housing has a base wall which extends substantially parallel to the UV-transmitting wall, and the housing has at least one reflecting side wall which extends from the base wall along the UV source at an angle to said base wall, and the reflecting side wall at a side facing the UV source comprises a material which has a comparatively low reflectivity to radiation with a wavelength  less than 320 nm. In this manner, only a small quantity of radiation with a wavelength  less than 320 nm is reflected by the side wall to the central area of the wall, so that the resulting effective radiation energy of this radiation in the central portion of the irradiation plane will be limited. This also benefits the homogeneous distribution of said effective radiation energy over the irradiation plane.
It is advantageous in this connection if said material has a comparatively high reflectivity to radiation with a wavelength in the range from 320 to 400 nm. Radiation with a wavelength in the range from 320 to 400 nm is thus reflected to a high degree towards the central area of the wall, which contributes to an optimum utilization of this radiation, in view of the small quantity of radiation produced by the UV source in this range.